1. Field of the Invention
The present invention relates to a semiconductor light emitting device; and, more particularly, to a semiconductor light emitting device capable of performing an operation at a high current and improving luminous efficiency by changing an arrangement structure of electrodes.
2. Description of the Related Art
Semiconductor light emitting devices contain materials emitting light inside. For example, LEDs (Light Emitting Diodes) are devices that use diodes, to which semiconductors are bonded, convert energy generated by recombination of electrons and holes into light, and emit the light. The semiconductor light emitting devices are being widely used as lighting, display devices, and light sources and the development thereof has been expedited.
In general, semiconductor junction light emitting devices have junction structures of p-type semiconductors and n-type semiconductors. In the junction structures of the semiconductors, light can be emitted by recombination of electrons and holes at junction regions of both types of semiconductors and further an active layer may be formed between both types of semiconductors in order to activate the light emission. The semiconductor junction light emitting devices have vertical structures and horizontal structures according to positions of electrodes for semiconductor layers and the horizontal structure includes an epi-up structure and a flip-chip structure.
FIG. 1 is a view showing a horizontal semiconductor light emitting device according to the related art and FIG. 2 is a cross-sectional view showing a vertical semiconductor light emitting device according to the related art. For the convenience of explanation, in FIGS. 1 and 2, a description will be made on the assumption that an n-type semiconductor layer is in contact with a substrate and a p-type semiconductor layer is formed on an active layer.
First, a horizontal semiconductor light emitting device will be described with reference to FIG. 1.
A horizontal semiconductor light emitting device 1 includes a non-conductive substrate 13, an n-type semiconductor layer 12, an active layer 11, and a p-type semiconductor layer 10. An n-type electrode 15 and a p-type electrode 14 are formed on the n-type semiconductor layer 12 and the p-type semiconductor layer 10, respectively and are electrically connected to an external current source (not shown) to apply a voltage or the like.
When the voltage is applied to the semiconductor light emitting device 1 through the electrodes 14 and 15, electrons move from the n-type semiconductor layer 12, and holes move from the p-type semiconductor layer 10, which results in recombination of the electrons and the holes to emit light. The semiconductor light emitting device 1 includes the active layer 11 and the light is emitted from the active layer 11. In the active layer 11, the light emission of the semiconductor light emitting device 1 is activated and the light is emitted. In order to make an electrical connection, the n-type electrode and the p-type electrode are positioned on the n-type semiconductor layer 12 and the p-type semiconductor layer 10, respectively, with the lowest contact resistance values.
The positions of the electrodes may be varied according to a substrate type. For instance, in case that the substrate 13 is a sapphire substrate that is a non-conductive substrate as shown in the drawing, the electrode of the n-type semiconductor layer 12 cannot be formed on the non-conductive substrate 13, but can be formed on the n-type semiconductor layer 12.
Therefore, when the n-type electrode 15 is formed on the n-type semiconductor 12, parts of the p-type semiconductor layer 10 and the active layer 11 that are formed at an upper side are consumed to form an ohmic contact portion. Because the electrodes are formed in this way, a light emitting area of the semiconductor light emitting device 1 is reduced, and thus luminous efficiency also decreases.
In order to address various problems including the above-described problem, a semiconductor light emitting device that uses a conductive substrate, not the non-conductive substrate, has appeared.
A semiconductor light emitting device 2 shown in FIG. 2 is a vertical semiconductor light emitting device. Since a conductive substrate 23 is used, an n-type electrode 25 can be formed on the substrate. Although, as shown in FIG. 2, the n-type electrode is formed on the conductive substrate 23, it is also possible to manufacture a vertical light emitting device by growing semiconductor layers by using a non-conductive substrate, removing the substrate, and then directly forming an n-type electrode on the n-type semiconductor layer.
When the conductive substrate 23 is used, because a voltage can be applied to an n-type semiconductor layer 22 through the conductive substrate 23, an electrode can be directly formed on the substrate.
Therefore, as shown in FIG. 2, the n-type electrode 25 is formed on the conductive substrate 23 and a p-type electrode 24 is formed on a p-type semiconductor 20, thereby manufacturing a semiconductor light emitting device having a vertical structure.
However, in this case, particularly, in case that a high-power light emitting device having a large area is manufactured, an area ratio of the electrode to the substrate needs to be high for current spreading. As a result, light extraction is limited, light loss is caused due to optical absorption, and luminous efficiency is reduced.
The horizontal and vertical semiconductor light emitting devices, which are described with reference to FIGS. 1 and 2, reduce the light emitting area to thereby reduce the luminous efficiency, limit the light extraction, cause the light loss due to the optical absorption, and reduce the luminous efficiency.
For this reason, a semiconductor light emitting device having a new structure needs to be urgently developed in order to solve the problems of the conventional semiconductor light emitting devices.